The present invention relates to a microwave resonant system having at least two resonant frequencies, such a resonant system being particularly provided for equipping a cyclotron intended for operation with two types of charged particles (deutons and protons for example).
In a cyclotron, the frequency of rotation of a particle of mass m and charge q is related to the magnetic induction B by the relationship: EQU f.sub.o =2.pi.(m/q.multidot.B) (1)
The frequency f of the accelerating microwave electric field must be equal to the frequency f.sub.o or to a multiple of this frequency f.sub.o, i.e.: EQU f=k f.sub.o ( 2)
k being a whole number.
For a suitably chosen accelerating structure of the cyclotron, protons of mass m and deutons of mass 2m may be successively accelerated by means of an accelerating electric field of frequency f. In this case, the protons will be accelerated in the accelerating space (or spaces) at each period of the microwave electric field for example (k=1), whereas the deutons will only be accelerated every two periods of the accelerating electric field (k=2). Such a cyclotron does not need the value of the magnetic induction B to be changed, depending on the type of particles chosen, but the accelerating system must be able to operate in these two modes.
Furthermore, if the cyclotron is provided with an accelerating structure comprising a single semi-circular "Dee", the condition required for the particles to find at the level of the second interaction space an accelerating electric field, is that the time for these particles to travel a full revolution must be equal to an uneven number of half-periods of the frequency of the microwave signal injected into the accelerating structure (i.e. k=1 and k=3). The value of the magnetic induction will be determined as a consequence thereof. In this case the operation of the cyclotron will not be optimum for the two types of particles.
The resonant system of the present invention, which may operate on two resonant frequencies, enables a cyclotron to be constructed for successively accelerating two types of particles without modifying the magnetic induction.